[Hammarlund] Send receive swtich

[Richard Knoppow]

    A couple of things: The switch on the receiver allows it to 
be desensitized by an external switch, usually a set of contacts 
on the antenna relay. By leaving the switch in Receive its 
possible to listen to your own signal, sometimes desirable when 
using CW.
    Most commercial and navy operation was "duplex" that is, 
separate receiving and sending frequencies and different 
antennas, often in different locations in land installations. So 
there was no switching between receiver and transmitter. This is 
ideal for break-in. Typically hams use "simplex" that is 
receiving and transmitting on the same frequency usually with the 
same antenna. An antenna relay is necessary to keep the 
transmitter signal out of the receiver where it would damage the 
input circuits.
    Switching can be done by a hand operated switch of some sort 
or some automatic switching like VOX which can also be used on CW.
    As far as RF sensing, I presume you mean that there is some 
device at the antenna feed that detects the presents of a strong 
RF signal, as from the transmitter, and makes the change over. In 
fact, there are electronic T-R switches, originally developed for 
radar, which will do this. They have been used since the early 
1940s and adapted to HF work.
    My old station used a foot switch, which is often very handy 
(or should I say footy) but I also had a hand operated switch.
     While modern solid state equipment has many circuits not 
duplicated in tube gear a lot of the "new" ideas are actually 
quite old but were not economical or practical before solid state.
    Also, a Send-Receive switch, or "Standby" switch allows 
muting the receiver without changing any of its settings, 
sometimes useful.

On 12/6/2019 6:23 AM, ve4feb at gmx.ca wrote:
> Nice info guys.
> 
> Ive read about manual tr switch back in the day and im familiar 
> with the send recieve schematic on my 145a. It does make sense to 
> use manual tr switch, before the fancy and expensive rf sense 
> stuff today.
> 
> I just find it hard to imagine a us navy operator listening for 
> cw on the hammarlund and then reach for the send/receive swtich 
> to answer back. It is even more strange at least for me with the 
> hammarlund 145 having send-rec-cw.
> 
> 
> Regards
> Fernan


-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL